#include<stdio.h>
#include<math.h>
int main()
{
	double x1, x2, y1, y2, d;
	0<= x1, x2, y1, y2 <= 100;
	scanf("%lf %lf %lf %lf", &x1, &y1, &x2, &y2);
	d = sqrt((x1 - x2)*(x1 - x2)+(y1 - y2)*(y1 - y2));
	printf("%.2lf", d);
	
	return 0;
}
